Oxygen precipitation in heat-treated Czochralski-grown silicon single crystals has been investigated using γ-ray diffraction combined with small-angle neutron scattering and infrared absorption measurements. Diffuse scattering around the diffraction peaks was observed using γ-rays and this is associated with oxygen precipitation in the silicon lattice. The analysis of the diffuse scattering produces an average precipitate size in agreement with small-angle neutron scattering measurements.